[PATCH 05/14] sched: Move sched_class::prio_changed() into the change pattern

Peter Zijlstra
2025-09-10T16:00:41Z

Move sched_class::prio_changed() into the change pattern.

And while there, extend it with sched_class::get_prio() in order to
fix the deadline sitation.

Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
kernel/sched/core.c | 24 +++++++++++++-----------
kernel/sched/deadline.c | 20 +++++++++++---------
kernel/sched/ext.c | 8 +-------
kernel/sched/fair.c | 8 ++++++--
kernel/sched/idle.c | 5 ++++-
kernel/sched/rt.c | 5 ++++-
kernel/sched/sched.h | 7 ++++---
kernel/sched/stop_task.c | 5 ++++-
kernel/sched/syscalls.c | 9 ---------
9 files changed, 47 insertions(+), 44 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2167,12 +2167,6 @@ inline int task_curr(const struct task_s
return cpu_curr(task_cpu(p)) == p;
}

-void check_prio_changed(struct rq *rq, struct task_struct *p, int oldprio)
-{
- if (oldprio != p->prio || dl_task(p))
- p->sched_class->prio_changed(rq, p, oldprio);
-}
-
void wakeup_preempt(struct rq *rq, struct task_struct *p, int flags)
{
struct task_struct *donor = rq->donor;
@@ -7437,9 +7431,6 @@ void rt_mutex_setprio(struct task_struct
p->sched_class = next_class;
p->prio = prio;
}
-
- if (!(queue_flag & DEQUEUE_CLASS))
- check_prio_changed(rq, p, oldprio);
out_unlock:
/* Avoid rq from going away on us: */
preempt_disable();
@@ -10894,6 +10885,13 @@ struct sched_change_ctx *sched_change_be
.running = task_current(rq, p),
};

+ if (!(flags & DEQUEUE_CLASS)) {
+ if (p->sched_class->get_prio)
+ ctx->prio = p->sched_class->get_prio(rq, p);
+ else
+ ctx->prio = p->prio;
+ }
+
if (ctx->queued)
dequeue_task(rq, p, flags);
if (ctx->running)
@@ -10920,6 +10918,10 @@ void sched_change_end(struct sched_chang
if (ctx->running)
set_next_task(rq, p);

- if ((ctx->flags & ENQUEUE_CLASS) && p->sched_class->switched_to)
- p->sched_class->switched_to(rq, p);
+ if (ctx->flags & ENQUEUE_CLASS) {
+ if (p->sched_class->switched_to)
+ p->sched_class->switched_to(rq, p);
+ } else {
+ p->sched_class->prio_changed(rq, p, ctx->prio);
+ }
}
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -3071,23 +3071,24 @@ static void switched_to_dl(struct rq *rq
}
}

+static u64 get_prio_dl(struct rq *rq, struct task_struct *p)
+{
+ return p->dl.deadline;
+}
+
/*
* If the scheduling parameters of a -deadline task changed,
* a push or pull operation might be needed.
*/
-static void prio_changed_dl(struct rq *rq, struct task_struct *p,
- int oldprio)
+static void prio_changed_dl(struct rq *rq, struct task_struct *p, u64 old_deadline)
{
if (!task_on_rq_queued(p))
return;

- /*
- * This might be too much, but unfortunately
- * we don't have the old deadline value, and
- * we can't argue if the task is increasing
- * or lowering its prio, so...
- */
- if (!rq->dl.overloaded)
+ if (p->dl.deadline == old_deadline)
+ return;
+
+ if (dl_time_before(old_deadline, p->dl.deadline))
deadline_queue_pull_task(rq);

if (task_current_donor(rq, p)) {
@@ -3142,6 +3143,7 @@ DEFINE_SCHED_CLASS(dl) = {
.task_tick = task_tick_dl,
.task_fork = task_fork_dl,

+ .get_prio = get_prio_dl,
.prio_changed = prio_changed_dl,
.switched_from = switched_from_dl,
.switched_to = switched_to_dl,
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -4023,7 +4023,7 @@ static void reweight_task_scx(struct rq
p, p->scx.weight);
}

-static void prio_changed_scx(struct rq *rq, struct task_struct *p, int oldprio)
+static void prio_changed_scx(struct rq *rq, struct task_struct *p, u64 oldprio)
{
}

@@ -5015,9 +5015,6 @@ static void scx_disable_workfn(struct kt
p->sched_class = new_class;
}

- if (!(queue_flags & DEQUEUE_CLASS))
- check_prio_changed(task_rq(p), p, p->prio);
-
scx_exit_task(p);
}
scx_task_iter_stop(&sti);
@@ -5766,9 +5763,6 @@ static int scx_enable(struct sched_ext_o
p->sched_class = new_class;
}

- if (!(queue_flags & DEQUEUE_CLASS))
- check_prio_changed(task_rq(p), p, p->prio);
-
put_task_struct(p);
}
scx_task_iter_stop(&sti);
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -13122,11 +13122,14 @@ static void task_fork_fair(struct task_s
* the current task.
*/
static void
-prio_changed_fair(struct rq *rq, struct task_struct *p, int oldprio)
+prio_changed_fair(struct rq *rq, struct task_struct *p, u64 oldprio)
{
if (!task_on_rq_queued(p))
return;

+ if (p->prio == oldprio)
+ return;
+
if (rq->cfs.nr_queued == 1)
return;

@@ -13138,8 +13141,9 @@ prio_changed_fair(struct rq *rq, struct
if (task_current_donor(rq, p)) {
if (p->prio > oldprio)
resched_curr(rq);
- } else
+ } else {
wakeup_preempt(rq, p, 0);
+ }
}

#ifdef CONFIG_FAIR_GROUP_SCHED
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -504,8 +504,11 @@ static void switching_to_idle(struct rq
}

static void
-prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio)
+prio_changed_idle(struct rq *rq, struct task_struct *p, u64 oldprio)
{
+ if (p->prio == oldprio)
+ return;
+
BUG();
}

--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2437,11 +2437,14 @@ static void switched_to_rt(struct rq *rq
* us to initiate a push or pull.
*/
static void
-prio_changed_rt(struct rq *rq, struct task_struct *p, int oldprio)
+prio_changed_rt(struct rq *rq, struct task_struct *p, u64 oldprio)
{
if (!task_on_rq_queued(p))
return;

+ if (p->prio == oldprio)
+ return;
+
if (task_current_donor(rq, p)) {
/*
* If our priority decreases while running, we
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2426,8 +2426,10 @@ struct sched_class {

void (*reweight_task)(struct rq *this_rq, struct task_struct *task,
const struct load_weight *lw);
+
+ u64 (*get_prio) (struct rq *this_rq, struct task_struct *task);
void (*prio_changed) (struct rq *this_rq, struct task_struct *task,
- int oldprio);
+ u64 oldprio);

unsigned int (*get_rr_interval)(struct rq *rq,
struct task_struct *task);
@@ -3852,12 +3854,11 @@ extern void set_load_weight(struct task_
extern void enqueue_task(struct rq *rq, struct task_struct *p, int flags);
extern bool dequeue_task(struct rq *rq, struct task_struct *p, int flags);

-extern void check_prio_changed(struct rq *rq, struct task_struct *p, int oldprio);
-
extern struct balance_callback *splice_balance_callbacks(struct rq *rq);
extern void balance_callbacks(struct rq *rq, struct balance_callback *head);

struct sched_change_ctx {
+ u64 prio;
struct task_struct *p;
int flags;
bool queued;
--- a/kernel/sched/stop_task.c
+++ b/kernel/sched/stop_task.c
@@ -81,8 +81,11 @@ static void switching_to_stop(struct rq
}

static void
-prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
+prio_changed_stop(struct rq *rq, struct task_struct *p, u64 oldprio)
{
+ if (p->prio == oldprio)
+ return;
+
BUG(); /* how!?, what priority? */
}

--- a/kernel/sched/syscalls.c
+++ b/kernel/sched/syscalls.c
@@ -95,12 +95,6 @@ void set_user_nice(struct task_struct *p
old_prio = p->prio;
p->prio = effective_prio(p);
}
-
- /*
- * If the task increased its priority or is running and
- * lowered its priority, then reschedule its CPU:
- */
- p->sched_class->prio_changed(rq, p, old_prio);
}
EXPORT_SYMBOL(set_user_nice);

@@ -708,9 +702,6 @@ int __sched_setscheduler(struct task_str
}
}

- if (!(queue_flags & DEQUEUE_CLASS))
- check_prio_changed(rq, p, oldprio);
-
/* Avoid rq from going away on us: */
preempt_disable();
head = splice_balance_callbacks(rq);